The present invention relates to a sealing method suited for sealing a liquid coolant into a module, a high-density module in particular, incorporated in a computer product such as a general-purpose computer, a server or the like.
A high-density module (hereinafter simply referred to as xe2x80x9cmodulexe2x80x9d) incorporated in a computer product such as a general-purpose computer, a server or the like is configured as a housing using a multilayer ceramic substrate as its base portion incorporating a plurality of electronic circuit parts such as ICs, LSIs or the like as its base portion. A heat-transferring liquid coolant is sealed in this housing. This module is mounted in a computer with the liquid coolant sealed in. The heat generated from the electronic circuit parts mounted in the multilayer ceramic substrate is radiated to the outside through the sealed liquid coolant, a comb-like microfin placed on the upper surface of the electronic circuit parts, a cooling material inserted between this microfin and the cover of the module, and an air-cooling fin placed on the top surface of the module.
Such a high-density module has a problem of air bubbles trapped in the liquid coolant sealed in. The module has many gaps, a gap between the electronic circuit parts and the substrate, a gap between the microfin and the cooling material, etc. It is difficult to completely fill these gaps with the liquid coolant, and air bubbles remain trapped in these gaps. The existence of these air bubbles prevents the effective cooling of heat generated from the electronic circuit parts. Reduced local cooling efficiency may cause the throughput of the electronic circuit parts to deteriorate.
One example of prior art known for solving this problem is disclosed in JP-A-9-213854 specification. This document discloses a method for sealing a liquid coolant with the following steps.
That is:
1. under a condition where a module is uncovered, fill the liquid coolant into the module beforehand;
2. place this module in a chamber that can be hermetically sealed;
3. reduce the pressure in the chamber to an approximate vacuum;
4. then, introduce an inert gas into the chamber and adjust the pressure inside the chamber to a pressure between an atmospheric pressure and the approximate vacuum;
5. hermetically seal the module in that state; and
6. increase the pressure inside the chamber to atmospheric pressure and seal the liquid coolant into the module.
This method allows air bubbles trapped in the liquid coolant filling the module to be eliminated when the pressure inside the chamber is reduced to the approximate vacuum.
As computer products become compact and their processing speed improved, electronic circuit parts mounted on modules are made with higher density and higher integration. This results in an increase in the number of connection terminal between LSIs and the substrate. Thus, both the diameter and pitch of the connection terminals such as solder balls, etc. are further becoming more fine. Therefore, gaps between the electronic circuit parts and the multilayer ceramic substrate are also being narrowed, and it is desired to eliminate air bubbles trapped inside these narrowed gaps.
Thus, it is an object of the present invention to provide a method for sealing a liquid into a module, which can seal the liquid into a high-density module housing a substrate on which high-density, highly integrated electronic circuit parts are mounted, with substantially no air bubbles trapped inside.
In order to attain the above object, according to the invention, a module housing a plurality of electronic circuit parts is placed in a chamber that can be hermetically sealed. The pressure inside the chamber is set to a liquid filling pressure between a vacuum pressure and atmospheric pressure, and the module is filled with a liquid. Then, the pressure inside the chamber is set to a sealing pressure between the liquid filling pressure and atmospheric pressure. In this state, the module is tightly sealed and the liquid is sealed in the module.
Furthermore, the above described sealing pressure is set so that the pressure inside the module becomes lower than atmospheric pressure even while the electronic circuit parts operate and the temperature of the sealing liquid in the module increases.